os_sup

Interface to OS System Messages

os_sup is a process providing a message passing service
from the operating system to the error logger in the Erlang
runtime system. It is part of the OS_Mon application, see
os_mon(6). Available for
Solaris and Windows.

Messages received from the operating system results in an
user defined callback function being called. This function can do
whatever filtering and formatting is necessary and then deploy any
type of logging suitable for the user's application.

Solaris Operation

The Solaris (SunOS 5.x) messages are retrieved from
the syslog-daemon, syslogd.

Enabling the service includes actions which require root
privileges, such as change of ownership and file privileges of an
executable binary file, and creating a modified copy of
the configuration file for syslogd. When os_sup is
terminated, the service must be disabled, meaning the original
configuration must be restored. Enabling/disabling can be done
either outside or inside os_sup, see
Configuration below.

Warning!

This process cannot run in multiple instances on the same
hardware. OS_Mon must be configured to start os_sup on
one node only if two or more Erlang nodes execute on the same
machine.

The format of received events is not defined.

Windows Operation

The Windows messages are retrieved from the eventlog file.

The nteventlog module is used to implement os_sup.
See nteventlog(3). Note
that the start functions of nteventlog does not need to be
used, in this case the process is started automatically as part of
the OS_Mon supervision tree.

Usually one of "System", "Application" or
"Security". Note that the NT eventlog viewer has
another notion of category, which in most cases is totally
meaningless and therefore not imported into Erlang. What is
called a category here is one of the main three types of
events occurring in a normal NT system.

Facility = string()

The source of the message, usually the name of
the application that generated it. This could be almost any
string. When matching messages from certain applications,
the version number of the application may have to be
accounted for. This is what the NT event viewer calls
"source".

Severity = string()

One of "Error", "Warning",
"Informational", "Audit_Success",
"Audit_Faulure" or, in case of a currently unknown
Windows NT version "Severity_Unknown".

Message = string()

Formatted exactly as it would be in the NT eventlog viewer.
Binary data is not imported into Erlang.

Configuration

os_sup_mfa = {Module, Function, Args}

The callback function to use. Module and
Function are atoms and Args is a list of terms.
When an OS message Msg is received, this function is
called as apply(Module, Function, [Msg | Args]).

Default is {os_sup, error_report, [Tag]} which will
send the event to the error logger using
error_logger:error_report(Tag, Msg). Tag is the value of
os_sup_errortag, see below.

os_sup_errortag = atom()

This parameter defines the error report type used when
messages are sent to error logger using the default callback
function. Default is std_error, which means the events
are handled by the standard event handler.

os_sup_enable = bool()

Solaris only. Defines if the service should be enabled (and
disabled) inside (true) or outside (false)
os_sup. For backwards compatibility reasons,
the default is true. The recommended value is
false, as the Erlang emulator should normally not be
run with root privileges, as is required for enabling
the service.

os_sup_own = string()

Solaris only. Defines the directory which contains
the backup copy and the Erlang specific configuration files
for syslogd, and a named pipe to receive the messages
from syslogd. Default is "/etc".

os_sup_syslogconf = string()

Solaris only. Defines the full name of the configuration file
for syslogd. Default is "/etc/syslog.conf".

Functions

enable() -> ok | {error, Res}

enable(Dir, Conf) -> ok | {error, Error}

Dir = Conf = Res = string()

Enables the os_sup service. Needed on Solaris only.

If the configuration parameter os_sup_enable is
false, this function is called automatically by
os_sup, using the values of os_sup_own and
os_sup_syslogconf as arguments.

If os_sup_enable is true, this function must
be called before OS_Mon/os_sup is started.
Dir defines the directory which contains the backup
copy and the Erlang specific configuration files for
syslogd, and a named pipe to receive the messages
from syslogd. Defaults to "/etc". Conf
defines the full name of the configuration file for
syslogd. Default is "/etc/syslog.conf".

Results in a OS call to:

<PRIVDIR>/bin/mod_syslog otp Dir Conf

where <PRIVDIR> is the priv directory of
OS_Mon, code:priv_dir(os_mon).

Returns ok if this yields the expected result
"0", and {error, Res} if it yields anything
else.

Note!

This function requires root privileges to succeed.

disable() -> ok | {error, Res}

disable(Dir, Conf) -> ok | {error, Error}

Dir = Conf = Res = string()

Disables the os_sup service. Needed on Solaris only.

If the configuration parameter os_sup_enable is
false, this function is called automatically by
os_sup, using the same arguments as when
enable/2 was called.

If os_sup_enable is true, this function must
be called after OS_Mon/os_sup is stopped.
Dir defines the directory which contains the backup
copy and the Erlang specific configuration files for
syslogd, and a named pipe to receive the messages
from syslogd. Defaults to "/etc". Conf
defines the full name of the configuration file for
syslogd. Default is "/etc/syslog.conf".

Results in a OS call to:

<PRIVDIR>/bin/mod_syslog nootp Dir Conf

where <PRIVDIR> is the priv directory of
OS_Mon, code:priv_dir(os_mon).

Returns ok if this yields the expected result
"0", and {error, Res} if it yields anything
else.